Abrasive article



Patented June 29, 1937 UNITED STATES PATENT OFFICE 2,085,137 ABRASIVEARTICLE No Drawing. Application December 8, 1933,

Serial N0. 701,532

, 9 Claims. (01. 51-278 This invention relates to an imprdvement1nthemanuiacture of abrasive articles and consistsin producing sucharticles having a' porous 'or'cellular structure.- 5 Abrasive articles,for example, grinding wheels, are, in general, made from graded abrasivegrains mixed with bonding materials. This mixture is moistened withwater, formed into the desired shape, dried and burned in a kiln. It 10has been the practice to'control the porosity of the article within alimited range of variation, by varying the grain size of the abrasivematerial, by varying the percentage of bond used, by the pressureapplied during the forming, by the 16 addition of wood fl6ur which.burns out leaving pore spaces, or by other'changes.

The present invention contemplates close control of the porosity andcell structure of finished abrasive articles by adding to the mix ofgranulated abrasive material and bond, granulated, oxidizable,non-compressible material which will burn away'during'the firing of thearticle inthe kiln leaving pores of a number and character theoxidiz'able, non-compressible material used.

An object of this invention, therefore, is to provide amethod of makingabrasive articles of a predetermined porosity and having pores orinterstices of a predetermined size.

Anotherobject is to provide a mix from which abrasive articles havingthe desired characteristics as to porosity and cell structure may bemade.

Other objects of the invention will be apparent from the followingdescription and appended claims.

The granulated material added to the mix as set forth above may be anysuitable material which, will not be compressed in the mix by thepressure used to form the abrasive articles and which will-burn awayduring the firing .of the articles in the kiln for example coke.

The granulated coke used may be mulled or not mulled as found desirablein use. If used directly as crushed and graded it will have veryirregular shapes with many sharp points and edges. It mulled, e. g.,-put through a slow revolving ball mill, the sharp corners and edges willbe worn ofi and the granules will be more rounded in shape and contour.

Any coke or related material, such as charcoal, may be used in carryingout the present invention, but for best results petroleum coke will befound desirable since it is relatively free from ash which might alterthe character of the bond. Depending upon the cellular structure desireddepending on the relative quantity and size of in the finished abrasivearticle the size of the granular coke may be smaller than, larger than,

I or equal to, that of the granular abrasive mate- Y rial used in themix. For grinding many mate- 'rials it may be necessary to have a highlyporous articlehaving a great numberof pores or interstices substantiallyequal to, or smaller than, the abrasive grains. To produce such anarticle it is desirable to use in the mix coke grains smaller than orsubstantially equal to the abrasive grains. in size. -'I'his does notmean, however, that the size of the pores in the finished article isequal to the size of the coke grains used, as the size of the pores isaiiected by other factors such as the nature and quantity oi the bondused and the degree of compression reached in forming the article. Bycontrolling these factors as well as the size of the coke grains thecellular structure of the finished article may be determined in ad:

vance.

When coke smaller than, or substantially the same size as the abrasivematerial is used, each abrasive grain in the finished article willcontact with practically all the adjacent grains as in the presentnon-porous articles, except that at intervals varying in frequency asthe degree of porosity desired, several grains will be so spaced as toprovide a void or interstice larger, than those formed by thevitrification of the bond but not substantially larger than each of theadjacent grains of abrasive.

For grinding other material it may' be-necessary to have an abrasivearticle wherein there are relatively large pores, compared to the sizeof the abrasive grains. The pores of such an article may be many timesthe size of the abrasive grains so that the walls of the pores areformed of a large number of abrasive grains. For the production of sucharticles it is necessary to add to the mix coke particles substantiallyequal to or larger than the abrasive grains. For. example, to produce anabrasive article having pores many times the size of the abrasive grainsit is necessary to use coke grainsmany times the size of the abrasiveparticles.

When coke is granulated the particles or granules formed takeveryirregular and diiierent shapes. When these particles are mixed in theabrasive article and subsequently burned out during the firing of thearticle the voids or interstices will in general take on substantiallythe shape of the particles of coke previously located therein. r

The proportion of granulated coke used in the mix is determined by thedegree of porosity de- 30 abrasive grams:

sired in the finished product. The amount may be as large as ispracticable to produce a porous article which is alsq strong enough forthe use for which it is intended. In preparing articles for mostpurposes the proportion of coke used is 5 to 30 percent by weight of theabrasive and bond used.

As an illustration of the invention a mix having the following formulamay be prepared and used to produce a porous abrasive article:

' Parts by weight Abrasive grain (80 grit) 85 Vitreous bond (through109) Calcined coke (40 on 74) 15 Temporary binder 2 Parts by weightAbrasive grain (40 grit) 85 Vitreous bond (through 109) 15 Calcined coke(through 40 on 74) Temporary binder 2 To produce an article having poressmaller than the abrasive grains the following formula could be used:

' Parts by weight Abrasive grain (40 grit) 85 Vitreous bond (through109) 15 Calcined coke (through 74 on 150) 20 Temporary binder 2 Thefollowing formula could be used to produce an article having pores manytimes the size of the abrasive grains used:

Parts by weight Abrasive grain (150 grit) a0 Vitreous bond (through 109)20 Calcined coke (through 40 on 74) 20 Temporary binder.. 2

. By means of the .present invention it is possible to economicallyproduce abrasive article's having any practicable number and shape ofcells. Articles which are light in weight and yet possess sufiicient'internal strength may be so produced. Because the use of coke increasesthe porosity and tends to spread out the abrasive grains 9.

relatively large proportion of bond may be used.

maintaining or increasing the internal strength, without increasing thetendency of the article to glaze in use. The use of coke or similarmaterial is advantageous in that it is not compressed by the pressureused to form the articles so that the form to which the mix is pressedwill not swell or spring back or otherwise lose its shape when pressureis released. Because the coke or other similar material will notcompress and can be accurately graded in advance the cell size can bedetermined in advance and produced without particularly'skillfulhandling. This method is easier and more accurate than, .for example, amethod employing gas bubbles to produce the voids or cells. Furthermore,a mixture employing coke is stable and does not have to be usedimmediately. Also, when coke is used to form the cells the cell wallstend to be more solid and less' porous while by the gas method the cellwalls tend to be porous due to minute gas bubbles contained therein.

It will be understood that the above description is not intended tolimit the scope of the invention herein but that the invention may beotherwise practiced or embodied without departing from the scope of theclaims.

We claim: a

1. A mix for making abrasive articles which containsgranular abrasivematerial, bond, and granulated coke.

2. A mix for making abrasive articles which comprises granular abrasivematerial and granulated coke having an average particle size at least asgreat as that of the abrasive material.

3. A mix for making abrasive articles which comprises granular abrasivematerial and granulated coke having an average particle size smallerthan that of the abrasive material.

4. A mix for making abrasive articles which consists of granularabrasive material, a vitreous bond, a temporary bond, water, andgranulated coke.

5. A mix for making abrasive articles which comprises granular abrasivematerial and granulated coke having an average particle size greaterthan that of the abrasive material.

6. In the process of making a bonded abrasive article the steps ofadding to the mix granulated coke, pressing the mixture to the desiredshape, and effecting removal of the coke granules by, firing the shapedarticle.

7. The process of making a bonded abrasive 7 article which comprisesintimately mixing granular abrasive material, suitable bondingmaterial,and granulated coke having an average particle size at least equaltothat of the'abrasive material, pressing the mixture to the desiredshape, and firing the same to burn away the coke granules and vitrifythe bond.

8. The process of making a bonded abrasive article which comprisesintimately mixing granular abrasive material, suitable bonding material,and granulated coke, having an average particle size several times asgreat as that of the abrasive material, pressing the mixture to thedesired shape, and firing the same to burn away the said oxidizablematerial and vitrify'the bond.

9. The process of making'a bonded abrasive article which comprisesintimately mixing granular abrasive material, suitable bonding material,and granulated coke having an average particle size smaller than that ofthe abrasive material, pressing themixture to the desired shape, andfiring the same to burn away the said granulated coke and vitrify thebond.

CHARLES E. WOODDELL. JOHN F. BARNES.

